To study with the collaboration of consulting pathologists, surgical specimens of neoplastic cells and tissues that are difficult to diagnose by conventional histologic and histochemical methods and/or those not previously described in the literature. In the present study of a surgical specimen of a solid tumor, a diagnosis of undifferentiated nasopharyngeal carcinoma of entodermal origin was made on the basis of ultrastructural and cytochemical studies differentiating the tumor cells from those of possible chordoma. Such studies that describe, characterize and identify aberrant neoplastic cells are an aid to prognosis and treatment.